It's pretty normal to score lower on the actual test than in practice, and it's pretty normal to get a mediocre result, so I don't see what this addendum would explain that your score history itself doesn't.

Is there any particular reason you struggle this much with standardized tests? You should identify it and either fix it or, if it's something like dysgraphia, petition LSAC for a testing accomodation. Then retake.

No. In a profession where one's professional school grades and license to practice is determined almost entirely by one's performance on tests, it's probably not helpful to highlight that you're "incapable of executing on test day."